YAHOOOO! Finally, something I really know something about! DianeB, I am a dog groomer, so I can help you out.
Most non-professional grooming kits have clippers with the clipon combs to get different lengths of hair. The first thing to do if you're gonna use that is to brush out your dog so there're no tangles for the comb to get stuck in, or at least get any tangles out enough from the skin so you can clip under them. Then give her a good bath, get her totally dry, and brush her out again. It's important to get oils and grit out of her hair so they don't mess up the clipper blade, and also so that her coat will be easier to clip.
Choose the comb for the length you want her coat, then, starting on her body, run the clipper along her body in the direction the hair grows (I'm assuming here that you just want her the same length all over). You may need to brush the hair forward and go over it several times to get it even.
As for the face, first brush the hair on top of the head up, and catch it between the pointer and middle finger of your other hand. With a pair of haircutting scissors, trim straight across over the top of those two fingers. Remember, you can always make it shorter, so err on the side of your fingers holding less hair at the top until you see how it looks (does that makes sense?)
For most terriers, the "Teddy Bear" face is what folks want. For this, first make sure you've combed out all the knots along her nose and chin. Comb the hair straight down, parted in the middle along her nose. Face her head on, then, starting on the right side, cut the hair in an broad U shape from the front of her chin to the back of her ear. Again, err on the side of longer until you get the look you want. Most dogs will hold relatively still for this if you gently hold the fur under their chin. Do the same on the left side. Then you're just going to trim straight across from one side to the other for the rest of the hair under her chin.
As for the ears.. well...if the hair needs trimming, just be sure you place your fingers on the end of the ear leather before you trim, so you know where it is and don't cut your puppy!
There are other things that might not be an issue with your dog, e.g. pulling hair from her ear canal, trimming in front of her eyes, doing a sanitary trim (so pee/poop don't get stuck in her fur), cleaning ears, trimming nails, and trimming hair from between paw pads. If you want, I can give you tips on any of these.
Just be sure to make this a good time with your dog, so she doesn't dread to see you coming at her with the clippers. Lots of calm, reassuring, comments and scratches behind the will probably do the trick. And, of course there's always the old bribe-with-a treat trick
Good luck! Post a picture!